The overall objective of this project is to elucidate the neural circuits responsible for implicit memory deficits in Parkinson's disease. The specific aims are to: 1. Investigate implicit memory impairments in patients with Parkinson's disease and to test whether a correlation exists between implicit memory deficits and motor deficits. 2. Develop a new implicit memory task to isolate non-motor deficits. 3. Use functional imaging to determine whether Parkinson's disease patients employ explicit memory systems to compensate for implicit memory deficits. 4. Test whether pallidotomy exacerbates implicit memory deficits and to test whether lesion size and location correlate with clinical outcome. The research methods will be based on implicit memory tasks validated in previous human memory studies. Structural MRI will be used to define the pallidotomy lesions and functional MRI will be used for functional imaging of subjects during implicit memory tasks. The proposed research will enhance our understanding of the neural circuits involved in implicit memory and provide new information on the effects of Parkinson's disease and pallidotomy on cognitive processes.